The purpose of this grant proposal is to request funds for partial support for the Sixth International Symposium on Chemistry and Biology of Pteridines in Relation to Chemotherapy to be held in La Jolla, California in September of 1978. Folic acid and biopterin derivatives are the most intensively investigated pteridines. Folic acid analogs such as Methotrexate and Trimethoprim are widely used therapeutically, the former for cancer and the latter for infectious disease. Biopterin is an essential cofactor for certain enzymatic hydroxylation reactions. The proposed Symposium will consist of individual research reports on the occurrence, chemistry, metabolism, function and chemotherapeutic aspects of pteridines. Although much infomation has been gathered in recent years on the mechanism of the chemotherapeutic effects of antifolates, the actual biochemical differences between susceptible and refractory cells is only now emerging. The objective of the Symposium is to bring together pteridine chemists, biochemists and chemotherapists from the United States and other countries to interact in a creative atmosphere and to document current advances in a Symposium volume.